Extensometer device



Dec. 19, 1939. Q. MOG. HENDERSON EXTENSOMETER DEVICE Filed July 16, 19362 Sheets-Sheet l Iii! Q l INVENTOR ATTOR N EYS Dec, 19, 1939. Q, MCG.HENDERSON EXTENSOMETER DEVICE Filed July 16, 193s /ll//ll//A IN VENTOR l2 Sheets-Sheet 2 www ATTOR N EYS Patented Dec. 19, 1939 T E aExrENscinemaJ DEVICE Quintin McGill Henderson, Kearny, N. J'., assignorto United States Steel Corporation, New

York, N. Y., a eorporationof New Jersey Applicatiqn July 16, 1936,seria1 N0..9o,9ss

2 Claims.

This inventionrelates to extensometer devices and to an improvementthereof adaptingl the same to measure the total strain or deformation ofa specimen tested in tension. Extensometer 5: devices are used in thetesting of materials under tension. VHeretofore in the art they havebeen adapted to determine the proportional limit and yield strength ofmaterials. It is frequently desired to obtain information `concerningthe behavior of such material between the yield point and rupture.

It is one of the objects of thisinvention to provide means to obtainthis information. Another object is to provide an extensometer deviceadapted to measure the total strain or deformation of a'materialup tothe point of rupture of the said material. Still another object of thisinvention is to provide an improved extens'ometer device in which alldanger of injury to the device through premature rupture of the materialbeing tested is eliminated. Other objects andadvantages will be apparentas the invention is more fully disclosed;

In accordance with these `objects I have devised an extensometer deviceconsisting of two telescoping sections adapted to be attached one ateach end of the specimen being tested, with means'to transmit therelative motion of the two telescoping parts representing the elongationof the specimen through a mechanism` whose final movement is exactlyproportional to this elongation, and means to magnify this proportionalmovement for purposes of indicating or recording the same.

The mechanism of the said transmitting means may be widely variedwithout departure from the present invention. It may comprise, forexample, a rack and pinionoperating a measuring cam; a bar and frictionwheel operating a measuring 40 screw; a racl; and pinion operating ameasuring drum; a rack and gear operating a measuring screw; or a wedgeoperating a measuring follower.

The means for magnifying this proportional movement of the mechanism ofthe said transmittingk means may also be varied extensively withoutdeparture from the present invention. It may comprise an electricalmeans, mechanical means or an optical means. For example, the electricalmeans may utilize a pair of selfsynchronizing motors adapted to transmitthe movement of the mechanically operating transmitting means to adistant indicating or recording apparatus capable of magnifying theresultant motion; the mechanical means may com- (Ci. 3?;-l4'7lvextensometer andthe indicating or recording apparatus; and the opticalmeans mayA comprise a rotatinglmirrorcr prismv in combination with meansto indicate or record the movement of the said'mirror or prism. o

Asone specific embodiment ofthe present invention I will" describe thesame utilizing the rack and pinion operating a measuring cam means fortransmitting the" relative movementv Vof the cam to an electricallyoperated means which actuates a reccrderdevice magnifying and recordingther movement of the cam.

AFigs. 1 2 and 3 of thefaccompanying drawings illustrate thisspecicembodimentflig. lbeing a front elevational view; Fig. 2 a sideelevational 15 View; andFig; 3y a bottomview of the same.

Referring to Figs. l, 2- and 3, the extensometer device -isshown-'in itsmounted position upon a specimen: :SiY ready-for testing. The two endsS- and vS" of thehspecimen are gripped in the usual manner byi meansprovided inthe usual vertical' type`-tensile testing'apparatus (notshown. In

such'te'stingdevice the. lower gripping means is stationary whiletheupper gripping means is movable vertically.

- The extensometerf device ofthe present invention comprises twoft'elescoping parts Ai and B.y The top partl frisv attached` to. thespecimen S at. a point above the point 'offrupture ofthe. specimenandthe bottom part B is attached t0 the .specimen S ata lpoint belowthepointof v rupture `of the specimen.

Thetop part A comprises a square section cross-bar. l with twohollow-cylinders 2 and'3 fastened one on" each end thereof .equidistantvfrom the center of bar l andat to its major axis.

On the upper face of the cross bar l is a hardened steel knife edge ll(Fig. `2)y with a concave face andV on the front-face of the bar I is abracket 5 (Fig. 3) carrying a sharp pointedv pinching screw 6. Togetherthe arrangement forms-the. means for attaching the top part A! tospecimen-S. The centers of the knifey edge 4 and screwtare coincidentwith the center line ofthe cross bar i. v

To the back face of the .bar l is fastened a straight toothed rack l,the pitch line :ofthe rack l' being disposed along ther centerline ofthe bar. l.' This rack 'l extends downwardly Afrom bar l beyondthebottom part Bj'substantially as indicated in Fig. 1.

Thebottcm part B Vcomprises a square section cross bar Bprovided withtwosolid cylinders-19 v andlffastened one oneach end `thereof equig5distant from the center of the bar 8 and at 90 to its major axis, insuch position relative to hollow cylinders 2 and 3 as to permit solidcylinders 9 and I0 to telescope within hollow cylinders 2 and 3. Means4', 5 and 6 (Figs. 2 and 3) substantially identical to the means 4, 5and 6 heretofore described with respect to the top part A are similarlyprovided on the bottom part BV for attaching the bottom part B to thespecimen S.

On the back face of bar 8 is disposed a spur gear Il, pivoted to the bar8 and engaging with the rack 'I extending downwardly from top part Awhen the extensometer device is in the closed position indicated in thedrawings. of this spur gear II is pinned cam I2 provided with a constantrise peripheral surface which rotates with spur gear II about the samecenter in the direction indicated by arrows in Fig. 1 when the two partsA and B are separated by being moved relative to each other along theaxes of cylinders 2-3 and 9-I0.

ABetween the solid cylinders S-IU and fastened to the inside face ofcross bar 8 is a short square rod I3 extending vertically upward uponthe top of which is disposed yoke I4 provided with an adjustable pivotscrew l5, the assembly forming a housing for pivoted lever I6, the freeend of which lever I6 extends downwardly past the cam I2. `A rider Il isfastened to the end of lever I6, and is held against the face of cam I2by the action of leaf spring I8. Any movement of cam l2 therefore istransmitted to lever IB.

Immediately adjacent rider I'I and movable therewith is disposed anelectrical contact I9. Fastened to the end of cross bar 8 is bracket 20comprised of insulating material, having a threaded opening therethroughhaving its axis parallel to the axis of bar 8 and in alignment withcontact I9 and at 90 to the pivoted lever I6. A spindle 2l is threadedthrough this threaded opening in bracket 20, upon the end of whichspindle 2i is provided an electrical contact 22 adapted to engagecontact I9 on lever I6.

The end of spindle 2| is connected by universal joint 23 to what isknown in the art as a selsyn motor which substantially comprises a pairof self-synchronizing motors electrically connected to be energized ordeenergized upon the making or breaking of an electrical contact (as atlil- 22) thereby causing a rotation of the spindle 2l which is forwardor reverse depending upon whether it is'desired to follow the movementof the contact I9 to thereby maintain an open or closed circuittherewith. In the instant case, it is desired to maintain electricalcontact between contacts I9 and 22. The motor means accordingly isconnected in suoli manner that as contact I9 is moved outwardly (to theleft Fig. 3) as indicated by dotted arrow thereby breaking electricalcontact with contact 22, the motor operates to actuate spindle 2I in thedirection adapted to close electrical connection between contacts I9 and22. The instant electrical connection is made, however, furtherenergizing of the motor means ceases until the circuit is again brokenby the movement of contact I9 to the left in the direction of the arrow.

This particular means of maintaining electrical connection betweencontacts I9 and 22 forms no part of the present invention and is a meansheretofore known in the art. The recording of the movement of contact I9by this particular means also forms no part ofthe present inven- To theface l tion, it heretofore having been adapted for this purpose.

In the practical use of the extensometer device as hereinabovedescribed, the two separated parts of the device are brought together inthe closed position indicated in Fig. l by turning spindle 2l backward adistance more than equal to the total rise obtained by cam. I2. The camI2 then is rotated by hand until the rider I'I on lever I6 is resting onthe edge of the highest part of cam I2. Rack 'I then is inserted in slot24 and engaged with gear II and the telescoping cylinders 2 3 and -I0brought into alignment and the two parts A and B pushed together. Inpushing the parts A and B together, rack 'I drives gear II therebyrotating cam I2 around to the point where rider Il rests against the lowpoint of the cam I2. The device then is in position for mounting uponthe specimen S.

When the electric current is connected to the recorder device the opencircuit across contacts I9 and 22 causes the selsyn motor -to operate torotate spindle 2I in a direction to close contacts I9 and 22 at whichclosing the motor is de-energized.

When load is applied to specimen S any stretch in the specimen istransmitted directly by rack 'I to gear II thence to cam. I2, whichrotates thereby pushing lever I6 to the left and moving contact I9 awayfrom contact 22 thereby breaking the electric circuit to the selsynmotor which immediately is energized to rotate spindle 2l thereby movingcontact 22 to a position adapted to close the circuit by making contactwith contact I9. This sequence continues until rupture occurs inspecimen S and the top part A pulls completely away from bottom part B.

The extensometer device of the present invention may be made in varioussizes adapting the same for use with different sizes of specimens S. Onestandard size specimen comprises sheet material having a two inch gaugelength by half inch width. The thickness of the sheet may vary up toabout eight gauge.

For this particular size specimen the length of hollow cylinders 2--3 isadapted to provide a distance of exactly two inches between knife edges4 4 when the device is in the closed position as shown. In order toobtain a recording of elongation of a two inch gauge length, gear II isprovided with a pitch diameter of .666 inch. The circumference of thispitch circumference would be 2.092 inches. As only two inches of thiscircumference is required the length of rack extending below thehorizontal diameter of gear Il is approximately two inches.

The cam I2, however, is designed for a slightly greater extension than 2inches. This feature allows a certain freedom in setting the startingpoint. This arrangement is purely arbitrary and is selected primarilybecause the recording apparatus is provided with-three rates of strainrecording of a ratio of l, 2 and 4. The chart paper is ten inches wide.On the low ratio eight (8)v revolutions of the selsyn motor is equal toten (10) inches of pen travel. The high rate equals forty (40) inches ofpen travel. I have merely selected eight (8) revolutions of the selsynmotor as being the most suitable number when a two (2) inch gauge lengthis being measured. This gives a strain magnification of 5, l0 and 20depending upon which rate is being used.

As spindle 2l is threaded lifty (50) threads to the inch, eight (8)revolutions would equal 50 inch or .160 inch which is the distance thespindle 2| advances in 100% elongation. Therefore the rise on cam l2should be .160 inch of each two (2) inch pitch circumference of gear Il.

As a second spe'c embodiment of the present invention reference shouldbe made to the drawings Figs. 4, 5 and 6. The separable parts A and B ofthe extensometer device are substantiaily identical to that heretoforedescribed in the embodiment of Figs. 1, 2 and 3. I have replaced therack l, gear II and cam I2 and associated means for moving Contact I9away from contact 22 with what is known as a bar and frictic-n wheelarrangement operating a measuring screw.

Referring to Figs. 4, 5 and 6, in place of rack 'I on the top part A (asin Figs. 1, 2 and 3) I provide a friction bar 36. On the bottom part B Iprovide a friction wheel 3l disposed in such position as to ride on bar3!! and to be rotated thereby. Means 32 are provided to transmit thero-tary motion of friction wheel 3! to measuring screw 33, on one end ofwhich is disposed electrical contact I9. Spindle 2I is mounted similarlyas heretofore described with respect to Figs. 1, 2 and 3 and carries onthe end thereof contact 22, which spindle 2l is actuated throughuniversal joint 23 by the selsyn motor arrangement as heretoforedescribed.

rilhis arrangement of elements has many advantages over that of themodiiication illustrated in Figs. 1, 2 and 3, but is not adapted forextreme sensitivity in measuring which is often desired in experimentalresearch work.

In place of the rack and pinion operating a measuring cam arrangement ofFigs. 1, 2 and 3 or the bar and friction wheel operating a measuringscrew arrangement of Figs. 4, 5 and 6, Imay adapt the other equivalentmechanisms above identified to the purpose of the present invention.

Having broadly and specifically described the present invention andhaving given two specific embodiments thereof, it is apparent that manymodifications' and adaptations may be made without essentially departingfrom the present inventionl and all such modifications and adaptationsare contemplated as may fall within the scope of the following claims.

What I claim is: n

1. An extensometer device comprising two separable and telescopinglparts each provided with means to attach the part to a specimen beingtested under tension at opposite sides of the point of rupture thereof,mechanism including a rack attached to one of said parts, a pinion gearattached to the other of said parts in a position to engage said rack,and a cam actuated by said gear to operate a movable contact a distancebearing a direct ratio to the distance traveled by said rack incident toa separating of said parts through the stretching of said material andmeans cooperating with said movable contact to record the movement ofthe same in magnified ratio.

2. An extensometer device comprising two separable and telescopingparts' each provided with means to attach the part to a specimen beingtested under tension at opposite sides of the point of rupture thereof,mechanism including a rack attached to one of said parts, a lpinion gearattached to the other of said parts in a position to engage said rack,and a cam actuated by said gear to operate a movable contact a distance

